Separation of sulphur dioxide and low-boiling hydrocarbons from mixtures thereof



Se t. 4, i945. a. w. HOOKER ETAL 2,334,373

SEPARATION OF SULPHUR DIOXIDE -AND LOW BOILING HYDROCARBONS FROM MIXTURES THEREOF Filed Nov. 3, 1941 y Fran Lana ea Patented Sept. 4, 1945 saranarron or SULPHUR moxmn asp LOW-BOILING nrnnocaanons mom MIXTURES 'rnnnaor George W. Hooker and Franc A. Landee, Midland, Mich asslgnors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application November 3, 1941, Serial No. 417,676

* 4 Claims. '(01. ca -17s).

This invention concerns an improved method of separating sulphur dioxide from mixtures thereof with low boiling aliphatic hydrocarbons, e. 3.,

from aliphatic hydrocarbons containing five or less carbon atoms in the molecule. It particuiar-.

ly concerns the separation of mixtures of sulphur dioxide and conjugated diolefines to recover each in anhydrous and purified form.

Buch mixtures of sulphur dioxide and low boiling, e. g., normally gaseous, hydrocarbonsare obtained in the known method for recovering diolefines from hydrocarbon mixtures by treatment,

with sulphur dioxide to form sulphones of the di' oleflnes. For instance, when a mixture of hutanes, butylenes, butadiene-L3, methyl acetylene,

' ethyl acetylene, and vinyl acetylene, such as is obtainable as a fraction of cracked-oil gas, is treated with sulphur dioxide at a liqueiying pressure in accordance with said known method, sulphur dioxide and butadiene react together to form a sulphone, from which a mixture of excess sulphur dioxide and the unreacted hydrocarbons are removed, e. g., by vaporization. .The sulphone is then thermally decomposed to form a mixture of sulphur dioxide and butadiene. Other mixtures of sulphur dioxide and low boiling or normally gase-- ous hydrocarbons are obtained by such treatment ofcrude cracked-oil gas itself, or other diolefine-containing fractions thereof, e. g.. the fraction containing isoprene and other hydrocarbons having five carbon atoms in the molecule, with sulphur dioxide to separate the diolefine from the other hydrocarbons.

Although sulphur dioxide may be removed from such mixtures with low boiling hydrocarbons by scrubbing with water, this is disadvantageous since the aqueous sulphurous acid so-formed is corrosive to usual metal equipment and such procedure necessitates extra steps for drying the sulphur dioxide if the latter is to be re-employed in the process. Because of the corrosiveness of the sulphurous acid formed and the quite low solubility of sulphur dioxide in water, expensive corrosion-resistant equipment of large size is required. Also the heat consumed in vaporizing siilphur dioxide from the dilute aqueous extract adds considerably to the cost of the recovery.

be separated from the hydrocarbons in such mixtures more conveniently and economically than by extraction with water, and whereby the sulphur dioxide and the hydrocarbons may each be recovered in substantially anhydrous condition.

Another object is to provide such method, whereby the size of extraction equipment required for the production of purified sulphur dioxide at a given rate may be reduced below that required when using water as the extractant. Other objects will be apparent from the following description of the invention.

Removal of the sulphur dioxide from the sulphur The invention comprises simultaneously extracting the sulphur dioxide and low boiling hydrocarbon mixture with two extractants, viz.,

with a liquefied organic sulphone and with a v normally liquid parafiln hydrocarbon of boiling point at least 20 C. above that of the low boiling hydrocarbons in the sulphur dioxide-hydrocarbon mixture to be separated. Such extractants are immiscible, or only partially soluble, in one another and have specific gravities which difier sufficiently to permit separation of the same as distinct layers on standing. The liquefied organic sulphones are shown in the co-pendlng application, Serial No. 290,864, of G. W. Hooker et al., to be exceptionally good solvents or absorbents for sulphur dioxide. They are poor solvents or non-solvents for the low boiling hydrocarbons. On the other hand, the liquid paraffln hydrocarbons are excellent solvents for the low boiling hydrocarbons to be separated from the sulphur dioxide and are non-solvents, or at best only poor solvents, for sulphur dioxide.

Examples of organic sulphones which may be employed in liquefied form as extractants in the process are diethyl sulphone, diisopropyl sul- U nents. Although any such liquefied sulphone,.

or mixture of sulphones, may be employed, the

sulphones of the conjugated diolefines are most readily available and are preferred. In the separation of sulphur dioxide from a mixture thereof with a diolefine, a sulphone of'the same diolefine is advantageously used as an extractant.

The sulphone extractant may be used in pure form, in which case the extraction must, of course,

be carried out at a temperature above its freezthe sulphones for the the agents suitable for 'of, each in the through the outlet 1 sulphones such as acetone, ethyl acetate, benzene,

ortho-dlchlorobenzene, methyl ethyl ketone, etc.

mixtures of such hydrocarbons, used as the extractant for the low boiiins hydrocarbons are hexane, tane, decane, and liquid fractions of petroleum such as gasoline. iisr in. solvent naphtha, kerosene, fuel oil, etc. The extractant is preferably introduced to the extraction in a form iree, or nearly so, of normally liquid aromatic or unsaturated hydrocarbons, e. g., benacne, toluene, higher oleiines, or higher acetylenes, etc., since the aromatic and unsaturated hydrocarbons are better solvents for sulphur dihydrocarbons and Although the extraction may be carried out in extraction may satisfactorily be carried out at batch-wise or continuous manner by agitating the sulphur dioxide and low boiling hydrocarbon mixture together with the two extractants in any of the usual ways and thereafter causing the resultant extracts to separate, e. g., by centrifuging or by settling into distinct layers on standing, it is advantageously carried out continuously within an extraction tower.

- The accompanying sketch of one of the various forms of extractors suitable for use in practicing the invention. In the drawing, the numeral I designates an extraction tower which may, but need not, be niled with Raschig rings, or other packing not shown. The tower is provided near its mid-section with an inlet 2 for the sulphur dioxide-hydrocarbon mixand the more dense tively. The inlet 4 preferably connects with a spray head l or a similar device within the tower for dispersing the'denser extractant as flne droplets in the less dense extractant, but such spray head may be omitted. The tower is also provided near its upperend with an outlet for one of the extracts and near its lower end with an 'outlet 1 for the other extract.

When using kerosene and the liquefied sulphone of butadiene-L3 as the extractants for the separation of a mixture of sulphur dioxide and butyla large extent upon the ene into its components. the valve in outlet I may be closed and the tower filled to overflowing with kerosene introduced through inlet 3. Whil continuing the flow of kerosene, liquefied sulphone may be fed into'the tower through inlet 4 and spray head 8, whereby it is dispersed as drops which settle downward through the up-iiowins kerosene and coalesce as a distinct layer at the bottom of the tower. in outlet 1 is opened phone from tive rates at which the two extractants are led e limited solubility 75 other, the kerosene overflowing irom the tower through outlet 8 is substantially free of the sulphone and the sulphone withdrawn is substantially free of kerosene. Thus, the two extractants are caused to iiow countercurrently through the tower. It may be mentioned that the relative rates of flow of the two extractants may be varied widely and still maintain the condition of balance between the flows Just described.

After regulating the rates or flow of the extraotants, the mixture of sulphur dioxide and butylene is introduced in liquid or vapor form through inlet 2. The relative rates at which the two extractants and said mixture are introduced are regulated in such manner that the kerosene absorbs nearly all of the butylene andthe sulphone absorbs nearly all of the sulphur dioxide. The extraction may be carried out at atmospheric pressure or above and at any temperature between that ,at which the sulphone crystallizes and that at which it is thermally decomposed. Thus, the

atmospheric pressure and at room temperature arated is vaporized when first introduced into the tower and .the mixed vapors are scrubbed and absorbed by the countercurrent flow of extractants. However, the proportion of sulphur dioxide absorbed in the sulphone and also the proportion of low boiling hydrocarbons absorbed by the kerosene becomes greater as the pressure on the extraction mixture is raised. In practice we prefer to carry the extraction out at temperatures between 65. and 85? C. under a pressure sufficient to liquefy the entire extraction mixture. The pressure required for liquefaction is dependent to ratios of solutes to solvents, particularly the ratio by weight of sulphur dioxide to sulphone. When this latter ratio is low. e. g., 5 or may suii'ice to liquefy the mixture. When the ratio is highe e. g., 20 or more, the pressure required for liquefaction may be 5 atmospheres or more. Pressures far higher than those required to liqueiy the mixture, e. g., pressures or 20-30 atmospheres or By operating under these preferred conditions, the productive capacity of the tower may be increased, due to the increased absorption capacities of the extractants and to avoidance of a vapor phase. and possible crystallization and accumulation of sulphone within the tower may be avoided.

During such extraction with two selective soivents flowing countercurrent to one another. the solution of butylene in kerosene is scrubbed, as .it rises in the tower, with a downflow of freshly introduced sulphone which eifectively extracts sulphur dioxide therefrom. Likewise, the solution of sulphur dioxide and sulphone is scrubbed, as it descends flow of kerosene which extracts absorbed butylene therefrom. By careful operation a substantially pure solution of butylene and kerosene may be.

withdrawn continuously through outlet 8 and a solution of sulphur dioxide and sulphone which is substantially free of butsdiene may be the drawn through outlet I.

The solutes may be recovered from the respective extracts in any of the usual ways, e. g., by vaporization, or by treatment with chemical reagents which react with the solute to form an insoluble derivative of the latter. etc. In pracless, a pressure of 1-2 atmospheres higher, may be employed desired.

through the tower, by the upward;

assasre tice, absorbed butylene is preferably vaporized, e. by raising the temperature and/or lowering the pressure, from the kerosene to leave the latter in condition for recycling in the process. Absorbed sulphur dioxide is likewise preferably vaporized from its solution in the sulphone, leaving the sulphone in condition for recycling. Alternatively, the solution of sulphur dioxide and the sulphone may be cooled to crystallize the sulphone, after which sulphur dioxide may be illtered, decanted or vaporized away from the crystalline sulphone. The sulphur dioxide and butylene are each recovered in a purified or highly concentrated anhydrous form.

The method as just described may be applied in separating sulphur dioxide from its mixtures with other low boiling hydrocarbons. Thus it is effective in recovering sulphur dioxide from the mixtures thereof with 'low boiling parailinic,

. oleflnic, or acetylenic hydrocarbons which are often obtained as unreacted materials in the production of sulphones. It may alsobe applied with advantage in separating sulphur dioxide and dioleflnes from the mixtures thereof which are produced by the thermal decomposition of corre- ,applied, but are not to beconstrued as limiting its scope.

Example 1 I A vertical extraction tower of 6 inch intern diameter and i'eet in height and having inlets I, and I, spray head 0, and the outlets 6 and l under said pressure. the dissolved low boiling hydrocarbons were vaporized therefrom by heating Example 2 A liquefied mixture of sulphur dioxide and butadiene-L3, produced by the thermal decomposition of the purified sulphoneof butadiene, has been continuously and simultaneously extracted with the liquefied sulphone of butadiene and with kerosene, the procedure in carrying out the extraction and in recoveringthe sulphur dioxide and butadiene from the resultant extracts being similar to that described in Example 1. The extrac-, tion and subsequent vaporization operations are readily carried out'to recover the'anhydrous sulphur dioxide and the butadiene each in a form of 96 per cent purity or higher.

Other modes of applying the principle of the invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.-

- We therefore particularly point out and distinctly claim as our invention:

1. In a method for separating sulphur dioxide j from a normally gaseous mixture thereof with at least one low boiling aliphatic hydrocarbon having indicated in theaccompanying drawing was filled with a hydrocarbon extractant consisting of equal parts by volume of kerosene and solvent naphtha, which extractant was pumped into the tower through inlet 3 at a temperature of .70" C. and overflowed through outlet. 8. While continuing flow of the hydrocarbon extractant, the liquefied sulphone of butadiene-1.3 was introduced in steady flow under pressure and at a temperature of 80 C. through inlet 4 and spray head 5. A crude liquefied reaction mixture consisting of 37.8 per cent by weight, of the sulphone of-l butadiene-1.3, 39.5 per cent of,sulphur dioxide, 20.8 per cent of butylene and 1.9 per cent of butadiene-1.3 was pumped under pressure into the tower through inlet 2. The valves in outlets 8 and l were opened. sufllciently to permit continuous withdrawal of the hydrocarbon extract and the sulphone extract, respectively, and yet maintain the mixture within the tower under a pressure of about 200 pounds per square inch, gauge. The rates at which the several materials were pumpedinto the tower were 0.24 gallon per minute of the hydrocarbon extractant through inlet 3, 0.15 gallon per minute of the liquefied sulphone through inlet 4, and 2.5 pounds per minute of the liquefied reaction mixture through inlet 1. The pressure on the sulphone extract was reduced to approximately atmospheric pressure as it flowed from the tower through outlet 1 sure on the hydrocarbon extract was reduced to about 40 pounds per square inch as it flowed from the extraction tower through outlet 0 and, while vand it was at the same time heated to about i not more than 5 carbon atoms in the molecule, the steps which consist in passing a normally liquid paraflinic hydrocarbon extractant upwardly through a tower and a liquefied organic sulphone extractant downward through the tower counter I to the liquid parafiinic hydrocarbon, while at the same time passing said mixture of sulphur dioxide and the low boiling hydrocarbon into the tower at a point where the extractants are in counterflow to one another, the mixture within the tower being at a superatmospheric pressure suilicient to liquefy the same, whereby sulphur dioxide is selectively absorbed by the sulphone and the low boiling hydrocarbon is selectively absorbed by the paramnic hydrocarbon extractant and the resultant extracts are caused to separate irom one another.

2. In a method for separating sulphur dioxide from a mixture comprising the same and a butylene, the steps which consist in passing a normally liquid fraction of petroleum and a liquefied sulphone of a conjugated diolefine through a tower in counter now to one another while at the same time introducing said mixture comprising sulphur dioxide and the butylene into the tower at a point where the liquefied sulphone and the liquid petroleum fraction flow counter to one another, the

mixture within the tower being at a superatmosmolecule, the steps which consist in introducing! said mixture into a tower at a point near the mid-section of the latter while introducing 9. normally liquid traction of petroleum into the tower at a point near the lower end oi the same and introducing and dispersing a liqueiied sulphone of a coniusated dioleiine at a point near the top oi the tower and restricting iiow of liquids from the tower so that the mixture within the same is under a superatmospheric pressure suiiicient to maintain the same in liquid tom. and during said operations continuously withdrawing the resultant extract eomprisins the liquid petroleum fraction and the conJugated dioleflne from the upper portion 01' the tower and continuously withdrawing the resultant extract comprising the liqueiied sulphone and sulphur dioxide from a lower portion of the tower and vaporizing the solute from at least one of the extracts so obtained.

4. In a method oi. separating sulphur dioxide caused to separate from one another, and vaporisin: the solute irom at least one oi the extracts so obtained. I GEORGE W. HOOKER.

FRANC A. LANDEI. 

